diff --git a/Cargo.toml b/Cargo.toml
index e2d70c8..3866543 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -10,7 +10,7 @@ repository = "https://github.com/trussed-dev/ctap-types"
 [dependencies]
 arbitrary = { version = "1.3.2", features = ["derive"], optional = true }
 bitflags = "1.3"
-cbor-smol = "0.4"
+cbor-smol = { version = ">= 0.4.1, < 0.6", features = ["heapless-bytes-v0-3"] }
 cosey = "0.3.1"
 delog = "0.1"
 heapless = { version = "0.7", default-features = false, features = ["serde"] }
diff --git a/src/ctap2.rs b/src/ctap2.rs
index f69fa18..598d1d9 100644
--- a/src/ctap2.rs
+++ b/src/ctap2.rs
@@ -242,7 +242,7 @@ impl<'a, A: SerializeAttestedCredentialData, E: serde::Serialize> AuthenticatorD
 
         // the extensions data
         if let Some(extensions) = self.extensions.as_ref() {
-            cbor_smol::cbor_serialize_extending_bytes(extensions, &mut bytes)
+            cbor_smol::cbor_serialize_to(extensions, &mut bytes)
                 .map_err(|_| Error::Other)?;
         }